The present invention relates generally to a hydraulic transmission pump assembly and, more specifically, to a method and apparatus for providing a hydraulic transmission pump assembly having differential actuation that supplies hydraulic power to a vehicle transmission.
Generally speaking, land vehicles require a powertrain consisting of three basic components. These components include a power plant (such as an internal combustion engine), a power transmission, and wheels. The power transmission component is typically referred to simply as the xe2x80x9ctransmission.xe2x80x9d Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the vehicle.
Transmissions generally include one or more gear sets. One type of gear set commonly employed in automatic transmissions is a planetary gear set, named for the relative rotation of the xe2x80x9cplanet gearsxe2x80x9d that each rotate on their individual axis while revolving around a xe2x80x9csun gearxe2x80x9d. Planetary gear sets are made up of three components, all in constant mesh; a sun gear, a planetary carrier with planet gears, and a surrounding ring gear or internal gear. When one component is held stationary, and another component is rotated, the third component is driven at either a reduction, or an increase in speed, or a rotation in the opposite direction. The planetary gear sets that are commonly used in today""s automatic transmissions are actually xe2x80x9ccompound planetary gear setsxe2x80x9d because they are basically two planetary sets that have common parts. Most 3-speed transmissions, for example, use two ring gears, two planetary carriers, and a common sun gear that is axially long enough to mesh with both planetary carriers. By changing which components are rotated by the engine, and which components are xe2x80x9cheldxe2x80x9d, two different gear reductions (1st gear, and 2nd gear) and reverse, as well as a 1:1 ratio (third gear) can be obtained. Thus transmissions typically include a plurality of clutch or brake assemblies that are employed as holding mechanisms in the transmission.
One example of a device used as a xe2x80x9choldingxe2x80x9d mechanism in a transmission is a one-way clutch. One-way clutches have inner and outer races that allow relative rotation of the two races in one direction but lock together in the opposite rotational direction. In application, when the races are fixed on concentric shafts, the shafts will be held together in one rotational direction, and be able to freewheel in the other rotational direction.
Multi-disk pack friction clutches are another example of a clutch assembly that is commonly employed for this purpose in a transmission. The multi-disk pack friction clutch or brake assembly usually employs a clutch subassembly including a set of plates and a set of friction disks that are interleaved between one another. The plates and friction disks are bathed in a continual flow of lubricant. The clutch or brake assembly also typically includes an actuating piston. When a component of a gear set is to be held, as for example during a particular gear change, a piston is actuated so as to cause the plates and friction disks to come into contact with respect to one another. In certain applications, it is known to employ several one-way clutches or multi-disk pack friction devices in combination to establish different drive connections throughout the transmission to provide various gear ratios in operation, or to brake a component. Thus, it is necessary to provide lubrication to the gear sets and the holding and shifting devices within the transmission in order to ensure their smooth and efficient operation while avoiding undue wear. Additionally, the lubrication functions to remove excess heat and cool the internal components of the transmission to within acceptable designed operating temperatures.
Within the transmission, the multi-disk friction clutches, brake systems, and gear sets have traditionally relied on a continuous xe2x80x9csplashxe2x80x9d supply of coolant, typically an oil, known generally as automatic transmission fluid (ATF), to remove the heat generated during operation and lubricate various moving parts. To this end, the transmission typically includes a hydraulic pump that provides ATF under pressure to supply various components with the fluid pressure necessary to actuate, lubricate and cool such components. The transmission pump is powered by the vehicle""s engine through some manner of connection with an input shaft. The pump draws ATF from a reservoir, or sump, through a filter. The ATF pressure is typically regulated by means of a solenoid-actuated regulator valve. The solenoid actuates a valve member to produce a bias pressure in the main transmission pressure line based on a command voltage received from a control module. In this way, the fluid pressure and flow in the main transmission pressure line are regulated to a desired value. Alternatively, some transmissions employ a less complex mechanical spring biased pressure regulator for the same purpose.
By having the pump driven by a power input of the vehicle""s engine, the resulting ATF fluid flow from the pump through the transmission main line, in both pressure and quantity, is proportional, or xe2x80x9clinearxe2x80x9d, with respect to engine speed. Conversely, the transmission generally requires ATF at constant volume and pressure across its operating range. Since conventional transmission pumps are driven by the vehicle engine, the conventional transmission pump and its mechanical drive components are sized so as to meet all possible lubrication, actuation and cooling requirements of the transmission when the engine, and thereby the pump mechanism, is at idle. Thus, whenever the engine speed is elevated above idle, the transmission pump produces a greater volume and pressure of ATF than is required and the supply of ATF is excessive. This excess amount of ATF flow is simply returned to the sump, by the regulator valve, as wasted energy. This wasted energy is an unnecessary mechanical loss that drains power from the engine, reducing transmission and overall vehicle efficiency.
Looking further ahead to new technological advances in automotive design, hybrid vehicles with multiple power sources and multiple power transfer operating modes are emerging. Hybrid vehicle designs can provide both low emissions and improve fuel economy. In order to do this, some hybrid vehicle designs switch drive modes between electrical power and conventional engines in such a manner that the internal combustion engine may be below a standard, or conventional idle speed, or off, at times during vehicle operation. This could occur when there is no forward movement of the vehicle (e.g., at a stoplight), or when the vehicle is coasting, or when driven solely by the electrical power source. This highlights another disadvantage in conventional transmission pump designs; namely, with the internal combustion engine at a below idle condition, there is little, or no, ATF flow. Thus, there is a need in the art to meet the lubrication, cooling and actuation requirements of the transmission in a hybrid vehicle during these operating conditions.
This drawback to the conventional automatic transmission pump can also be seen in conventional vehicles in one other specific instance. If the engine is off in a conventional vehicle, yet the vehicle""s drivetrain is moving, for example where a vehicle is being towed, there is no ATF lubrication being provided to the bearings and gear sets of the transmission. Simply towing the vehicle could cause damage to the internal workings of the transmission itself.
In light of the above, those having ordinary skill in the art will appreciate that specific disadvantages to conventional transmission ATF pump construction and operation exist. The first being the excessive ATF flow delivery for engine speeds at or above idle, which results in a drain to the engine""s power resources and second, the inability of conventional designs to adequately supply the transmission with ATF during engine off or below idle conditions. These disadvantages create the need for a transmission pump design that is both more efficient and is able to operate when the vehicle""s engine is below idle, off, or otherwise disconnected, but transmission and thereby vehicle operation is required.
The hydraulic transmission pump assembly of the present invention overcomes the disadvantages in the related art as a pump adapted to provide fluid under pressure to predetermined components in a transmission. The hydraulic transmission pump assembly includes an electric motor operatively coupled to the pump and a differential gear assembly interposed between an engine and the electric motor. The differential gear assembly acts to divide engine torque between the pump and the electric motor at engine speeds above a predetermined level thereby providing fluid under pressure to the transmission and driving the electric motor to generate electricity. The electric motor is operable to drive the pump at engine speeds below the predetermined level thereby providing fluid under pressure to the transmission during this operating condition.
The present invention is also directed toward a method of providing hydraulic power to an automotive transmission. The method includes the steps of providing a pump which is operatively actuated about a central axis as defined by a common driven shaft, providing an electric motor which is electrically connected to the electrical system of an automobile, and providing a differential gear assembly interposed between a power input and the electric motor. The method also includes the steps of controlling the operation of the differential gear assembly such that the differential gear assembly causes the pump to be driven by the electric motor when the automotive engine is operating below a predetermined RPM, and controlling the differential gear assembly such that it causes both the pump and the electric motor to be driven by the power input when the automotive engine is operating above a predetermined RPM such that the electric motor functions as a generator to provide electric power back to the automobile electrical system during specific times of motor vehicle operation.
Therefore, the present invention overcomes the drawbacks and disadvantages of the related art, which cannot provide the proper ATF flow to the transmission when the vehicle engine is off or below idle speed. Additionally, the present invention is more efficient than the prior art as it provides the required, regulated ATF flow anytime the engine is at idle or above, while concurrently converting any excess applied engine power into usable electrical energy that is fed back to the vehicle electrical system.